Selective membrane having a high fouling resistance

ABSTRACT

A selective membrane having a high fouling resistance. In one embodiment, the selective membrane is a composite polyamide reverse osmosis membrane having a hydrophilic coating made by covalently bonding a hydrophilic compound to the polyamide membrane, the hydrophilic compound including (i) a reactive group that is adapted to covalently bond directly to the polyamide membrane, the reactive group being at least one of a primary amine and a secondary amine; (ii) a non-terminal hydroxyl group; and (iii) an amide group. In another embodiment, the hydrophilic compound includes (i) a reactive group adapted to covalently bond directly to the polyamide membrane, the reactive group being at least one of a primary amine and a secondary amine; (ii) a hydroxyl group; and (iii) an amide group, the amide group being linked directly to the hydroxyl group by one of an alkyl group and an alkenyl group.

BACKGROUND OF THE INVENTION

The present invention relates generally to selective membranes andrelates more particularly to selective membranes having a high foulingresistance.

It is known that dissolved substances can be separated from theirsolvents by the use of various types of selective membranes, suchselective membranes including—listed in order of increasing poresize—reverse osmosis membranes, ultrafiltration membranes andmicrofiltration membranes. One use to which reverse osmosis membraneshave previously been put is in the desalination of brackish water orseawater to provide large volumes of relatively non-salty water suitablefor industrial, agricultural or home use. What is involved in thedesalination of brackish water or seawater using reverse osmosismembranes is literally a filtering out of salts and other dissolved ionsor molecules from the salty water by forcing the salty water through areverse osmosis membrane whereby purified water passes through themembrane while salts and other dissolved ions and molecules do not passthrough the membrane. Osmotic pressure works against the reverse osmosisprocess, and the more concentrated the feed water, the greater theosmotic pressure which must be overcome.

A reverse osmosis membrane, in order to be commercially useful indesalinating brackish water or seawater on a large scale, must possesscertain properties. One such property is that the membrane have a highsalt rejection coefficient. In fact, for the desalinated water to besuitable for many commercial applications, the reverse osmosis membraneshould have a salt rejection capability of at least about 97%. Anotherimportant property of a reverse osmosis membrane is that the membranepossess a high flux characteristic, i.e., the ability to pass arelatively large amount of water through the membrane at relatively lowpressures. Typically, the flux for the membrane should be greater than10 gallons/ft²-day (gfd) at a pressure of 800 psi for seawater andshould be greater than 15 gfd at a pressure of 220 psi for brackishwater. For certain applications, a rejection rate that is less than thatwhich would otherwise be desirable may be acceptable in exchange forhigher flux and vice versa.

One common type of reverse osmosis membrane is a composite membranecomprising a microporous support and a thin polyamide film formed on themicroporous support. Typically, the polyamide film is formed by aninterfacial polymerization of a polyfunctional amine and apolyfunctional acyl halide.

An example of the aforementioned composite polyamide reverse osmosismembrane is disclosed in U.S. Pat. No. 4,277,344, inventor Cadotte,which issued Jul. 7, 1981, and which is incorporated herein byreference. The aforementioned patent describes an aromatic polyamidefilm which is the interfacial reaction product of an aromatic polyaminehaving at least two primary amines substituents with an aromatic acylhalide having at least three acyl halide substituents. In the preferredembodiment, a porous polysulfone support is coated withm-phenylenediamine in water. After removal of excess m-phenylenediaminesolution from the coated support, the coated support is covered with asolution of trimesoyl chloride dissolved in “FREON” TF solvent(trichlorotrifluoroethane). The contact time for the interfacialreaction is 10 seconds, and the reaction is substantially complete in 1second. The resulting polysulfone/polyamide composite is then air-dried.

Although the Cadotte membrane described above exhibits good flux andgood salt rejection, various approaches have been taken to furtherimprove the flux and salt rejection of composite polyamide reverseosmosis membranes. In addition, other approaches have been taken toimprove the resistance of said membranes to chemical degradation and thelike. Many of these approaches have involved the use of various types ofadditives to the solutions used in the interfacial polycondensationreaction.

For example, in U.S. Pat. No. 4,872,984, inventor Tomaschke, whichissued Oct. 10, 1989, and which is incorporated herein by reference,there is disclosed an aromatic polyamide membrane formed by (a) coatinga microporous support with an aqueous solution comprising (i) anessentially monomeric, aromatic, polyamine reactant having at least twoamine functional groups and (ii) a monofunctional, monomeric (i.e.,polymerizable) amine salt to form a liquid layer on the microporoussupport, (b) contacting the liquid layer with an organic solventsolution of an essentially monomeric, aromatic, amine-reactive reactantcomprising a polyfunctional acyl halide or mixture thereof, wherein theamine-reactive reactant has, on the average, at least about 2.2 acylhalide groups per reactant molecule, and (c) drying the product of step(b), generally in an oven at about 60° C. to 110° C. for about 1 to 10minutes, so as to form a water permeable membrane.

Other patents disclosing the use of additives in the solutions employedin the interfacial polycondensation reaction include: U.S. Pat. No.4,983,291, inventors Chau et al., which issued Jan. 8, 1991; U.S. Pat.No. 5,576,057, inventors Hirose et al., which issued Nov. 19, 1996; U.S.Pat. No. 5,614,099, inventors Hirose et al., which issued Mar. 25, 1997;U.S. Pat. No. 4,950,404, inventor Chau, which issued Aug. 21, 1990; U.S.Pat. No. 4,830,885, inventors Tran et al., which issued May 16, 1989;U.S. Pat. No. 6,245,234, inventors Koo et al., which issued Jun. 12,2001; U.S. Pat. No. 6,063,278, inventors Koo et al., which issued May16, 2000; and U.S. Pat. No. 6,015,495, inventors Koo et al., whichissued Jan. 18, 2000, all of which are incorporated herein by reference.

Another approach which has been taken to improve the performance of acomposite polyamide reverse osmosis membrane is disclosed in U.S. Pat.No. 5,178,766, inventors Ikeda et al., which issued Jan. 12, 1993, andwhich is incorporated herein by reference. According to Ikeda et al.,the salt rejection rate of a composite polyamide reverse osmosismembrane is said to be improved by covalently bonding to the polyamidefilm of said membrane a compound having a quaternary nitrogen atom. Saidquaternary nitrogen atom-containing compound is bonded to the polyamidefilm through a reactive group present in the compound, said reactivegroup being an epoxy group, an aziridine group, an episulfide group, ahalogenated alkyl group, an amino group, a carboxylic group, ahalogenated carbonyl group, or a hydroxy group.

One problem encountered by many of the various composite polyamidereverse osmosis membranes described above is fouling, i.e., theundesired adsorption of solutes to the membrane, thereby causing areduction in flux exhibited by the membrane. Fouling is typically causedby hydrophobic-hydrophobic and/or ionic interactions between thepolyamide film of the membrane and those solutes present in the solutionbeing filtered. As can readily be appreciated, fouling is undesirablenot only because it results in a reduction in flux performance for themembrane but also because it requires that operating pressures be variedfrequently to compensate for the variations in flux experienced duringsaid reduction. In addition, fouling also requires that the membrane becleaned frequently.

One approach to the problem of fouling is disclosed in U.S. Pat. No.6,177,011, inventors Hachisuka et al., which issued Jan. 23, 2001, andwhich is incorporated herein by reference. According to Hachisuka etal., fouling can be reduced by coating the polyamide film of themembrane with at least one substance selected from the group consistingof an electrically neutral organic substance and a polymer that has anonionic hydrophilic group, said organic substance or polymer preferablybeing a polyvinyl alcohol.

Another approach to the problem of fouling is disclosed in U.S. Pat. No.6,280,853, inventor Mickols, which issued Aug. 28, 2001, and which isincorporated herein by reference. Mickols discloses a composite membranethat is said to have an improved resistance to fouling, said compositemembrane comprising a porous support and a crosslinked polyamide surfacehaving polyalkylene oxide groups grafted thereto.

Yet another approach to the problem of fouling is disclosed in U.S.Patent Application Publication No. US 2010/0143733 A1, inventors Mickolset al., which was published Jun. 10, 2010, and which is incorporatedherein by reference. Mickols et al. discloses a polyamide membrane andmethod for making and using the same. According to one embodiment, apolyamide membrane includes a coating comprising a combination of apolyalkylene oxide compound and a polyacrylamide compound.

Still another approach to the problem of fouling is disclosed in U.S.Pat. No. 6,913,694, inventors Koo et al., which issued Jul. 5, 2005, andwhich is incorporated herein by reference. Koo et al. discloses aselective membrane having a high fouling resistance. In one embodiment,the selective membrane is a composite polyamide reverse osmosis membranein which a hydrophilic coating has been applied to the polyamide layerof the membrane, the hydrophilic coating being made by (i) applying tothe membrane a quantity of a polyfunctional epoxy compound, thepolyfunctional epoxy compound comprising at least two epoxy groups, and(ii) then, cross-linking the polyfunctional epoxy compound in such amanner as to yield a water-insoluble polymer.

Still yet another approach to the problem of fouling is disclosed inU.S. Pat. No. 7,537,697, inventors Koo et al., which issued May 26,2009, which is incorporated herein by reference. This patent discloses aselective membrane having a high fouling resistance. In one embodiment,the selective membrane is a composite polyamide reverse osmosis membranein which a hydrophilic coating is applied to the polyamide layer of themembrane, the hydrophilic coating being made by covalently bonding ahydrophilic compound to residual acid chlorides of the polyamidemembrane, the hydrophilic compound including (i) at least one reactivegroup that covalently bonds directly to the polyamide membrane, the atleast one reactive group being at least one of a primary amine and asecondary amine, and (ii) at least one hydrophilic group selected fromthe group consisting of a hydroxyl group, a carbonyl group, atrialkoxysilane group, an anionic group and a tertiary amino group;(iii) wherein the hydrophilic compound is devoid of a polyalkylene oxidegroup.

Still a further approach to the problem of fouling is disclosed in U.S.Pat. No. 7,913,857, inventors Koo et al., which issued Mar. 29, 2011,which is incorporated herein by reference. This patent discloses aselective membrane having a high fouling resistance. In one embodiment,the selective membrane is a composite polyamide reverse osmosis membranein which a hydrophilic coating is applied to the polyamide layer of themembrane, the hydrophilic coating being made by covalently bonding ahydrophilic compound to residual acid chlorides of the polyamidemembrane, the hydrophilic compound including (i) at least one reactivegroup that covalently bonds directly to the polyamide membrane, the atleast one reactive group being at least one of a primary amine and asecondary amine, and (ii) at least one non-terminal hydroxyl group.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel compositepolyamide reverse osmosis membrane.

It is another object of the present invention to provide a membrane asdescribed above that possesses high fouling resistance.

Accordingly, in furtherance of the above objects, as well as otherobjects to be described herein or to become apparent from thedescription that follows, there is provided a composite polyamidereverse osmosis membrane, said composite polyamide reverse osmosismembrane comprising, in a first aspect, (a) a microporous support; (b) apolyamide layer on said microporous support; and (c) a hydrophiliccoating on said polyamide layer, said hydrophilic coating being formedby covalently bonding a hydrophilic compound to the polyamide membrane,wherein said hydrophilic compound includes (i) at least one reactivegroup adapted to covalently bond directly to the polyamide membrane,said at least one reactive group being at least one of a primary amineand a secondary amine; (ii) at least one non-terminal hydroxyl group;and (iii) at least one amide group.

According to a first embodiment of said first aspect, the aforementionedhydrophilic compound may be a compound represented by the formula I:

R₁—(CHOH)₁—CONR₄—R₂—NHR₃  (I)

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of an alkyl group having carbon atoms ranging from 2 to 12, analkenyl group having at least one double bond and carbon atoms rangingfrom 2 to 12, a cyclohexyl group, a phenylene group, a xylylene group,and a cyclohexanebismethyl group, wherein R₃ is one of hydrogen, analkyl group having carbon atoms ranging from 1 to 4, and an alkenylgroup having at least one double bond and carbon atoms ranging from 2 to4, wherein R₄ is one of hydrogen, a methyl group, an ethyl group, and apropyl group, and wherein l is an integer ranging from 1 to 10.

According to a second embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula II:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), and whereinl is an integer ranging from 1 to 10.

According to a third embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula III:

R₁—(CHOH)₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (III)

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of hydrogen, an alkyl group having carbon atoms ranging from 1 to4, and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of hydrogen, a methyl group, anethyl group, and a propyl group, wherein l is an integer ranging from 1to 10, wherein m is an integer ranging from 1 to 1000, and wherein n isan integer ranging from 2 to 6.

According to a fourth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula IV:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of hydrogen, an alkyl group having carbon atoms ranging from 1 to4, and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of a methyl group and an ethylgroup, wherein l is an integer ranging from 1 to 10, wherein R₄ is oneof hydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 100.

According to a fifth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula V:

R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH₂O)_(m)—CH₂CH(OH)CH₂—NHR₂  (V)

wherein R₁ is one of hydrogen, a methyl group, and an ethyl group,wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 1000.

According to a sixth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula VI:

R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH(CH₃)O)_(m)—CH₂CH(OH)CH₂—NHR₂  (VI)

wherein R₁ is one of hydrogen, a methyl group, and an ethyl group,wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 100.

According to a second aspect of the invention, there is provided acomposite polyamide reverse osmosis membrane, said composite polyamidereverse osmosis membrane comprising (a) a microporous support; (b) apolyamide layer on said microporous support; and (c) a hydrophiliccoating on said polyamide layer, said hydrophilic coating being formedby covalently bonding a hydrophilic compound to the polyamide membrane,wherein said hydrophilic compound includes (i) at least one reactivegroup adapted to covalently bond directly to the polyamide membrane,said at least one reactive group being at least one of a primary amineand a secondary amine; (ii) a hydroxyl group; and (iii) an amide group;(iv) wherein the hydroxyl group and the amide group are linked directlyto one another by one of an alkyl group and an alkenyl group.

According to a first embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula VII:

HO—R₁—CONR₄—R₂—NHR₃  (VII)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is an alkyl group having carbonatoms ranging from 2 to 6, an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 6, a cyclohexyl group, aphenylene group, a xylylene group, and a cyclohexanebismethyl group,wherein R₃ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₄ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein NR₄—R₂—NHR₃ can be replaced with a piperazinyl group.

According to a second embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula VIII:

HO—R₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (VIII)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is one of hydrogen, an alkyl grouphaving carbon atoms ranging from 1 to 4, and an alkenyl group having atleast one double bond and carbon atoms ranging from 2 to 4, wherein R₃is one of hydrogen, a methyl group, an ethyl group, and a propyl group,wherein m is an integer ranging from 1 to 1000, and wherein n is aninteger ranging from 2 to 6.

According to a third embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula IX:

HO—R₁—CONR₃—(CH₂CH(CH₃)O)_(m)—CH₂CH(CH₃)—NHR₂  (IX)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is one of hydrogen, an alkyl grouphaving carbon atoms ranging from 1 to 4, and an alkenyl group having atleast one double bond and carbon atoms ranging from 2 to 4, wherein R₃is one of hydrogen, a methyl group, an ethyl group, and a propyl group,and wherein m is an integer ranging from 1 to 100.

The present invention is also directed to a method of producing theabove-described composite polyamide reverse osmosis membrane.

The present invention is further directed to microfiltration membranesand ultrafiltration membranes that include the high fouling resistancecoating of the present invention, as well as to a method of making suchcoated membranes.

Additional objects, features, aspects and advantages of the presentinvention will be set forth, in part, in the description which followsand, in part, will be obvious from the description or may be learned bypractice of the invention. Certain embodiments of the invention will bedescribed hereafter in sufficient detail to enable those skilled in theart to practice the invention, and it is to be understood that otherembodiments may be utilized and that structural or other changes may bemade without departing from the scope of the invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is best defined by the appendedclaims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As noted above, the present invention is based on the unexpecteddiscovery that the fouling resistance of a selective membrane, such as acomposite polyamide reverse osmosis membrane, a microfiltration membraneor an ultrafiltration membrane, can be significantly increased byapplying to the membrane a hydrophilic coating of the type describedbelow.

The composite polyamide reverse osmosis membrane to which thehydrophilic coating of the present invention is applied may be virtuallyany composite polyamide reverse osmosis membrane of the type comprisinga porous support and a polyamide film disposed on said porous support.

The aforementioned porous support is typically a microporous support.The particular microporous support employed is not critical to thepresent invention but is generally a polymeric material containing poresizes which are of sufficient size to permit the passage of permeatetherethrough but not large enough so as to interfere with the bridgingover of the ultrathin membrane formed thereon. The pore size of thesupport will generally range from 1 to 500 nanometers inasmuch as poreswhich are larger in diameter than 500 nanometers will permit theultrathin film to sag into the pores, thus disrupting the flat sheetconfiguration desired. Examples of microporous supports useful in thepresent invention include those made of a polysulfone, a polyethersulfone, a polyimide, a polyamide, a polyetherimide, polyacrylonitrile,poly(methyl methacrylate), polyethylene, polypropylene and varioushalogenated polymers, such as polyvinylidene fluoride. Additionalmicroporous support materials may be found in the patents incorporatedherein by reference.

The thickness of the microporous support is not critical to the presentinvention. Generally, the thickness of the microporous support is about25 to 125 μm, preferably about 40 to 75 μm.

The polyamide film of the present invention is typically the interfacialreaction product of a polyfunctional amine reactant and a polyfunctionalamine-reactive reactant. The polyfunctional amine reactant employed inthe present invention is preferably an essentially monomeric aminehaving at least two amine functional groups, more preferably 2 to 3amine functional groups. The amine functional group is typically aprimary or secondary amine functional group, preferably a primary aminefunctional group. The particular polyamine employed in the presentinvention is not critical thereto and may be a single polyamine or acombination thereof. Examples of suitable polyamines include aromaticprimary diamines, such as meta-phenylenediamine andpara-phenylenediamine and substituted derivatives thereof, wherein thesubstituent includes, e.g., an alkyl group, such as a methyl group or anethyl group, an alkoxy group, such as a methoxy group or an ethoxygroup, a hydroxy alkyl group, a hydroxyl group or a halogen atom.Additional examples of suitable polyamines include alkanediamines, suchas 1,3-propanediamine and its homologs with or without N-alkyl or arylsubstituents, cycloaliphatic primary diamines, cycloaliphatic secondarydiamines, such as piperazine and its alkyl derivatives, aromaticsecondary amines, such as N,N″-dimethyl-1,3-phenylenediamine,N,N″-diphenylethylene diamine, benzidine, xylylene diamine andderivatives thereof. Other suitable polyamines may be found in thepatents incorporated herein by reference. The preferred polyamines ofthe present invention are aromatic primary diamines, more preferablym-phenylenediamine, and piperazine. (A composite polyamide reverseosmosis membrane made using piperazine as the polyfunctional aminereactant falls within a subclass of composite polyamide reverse osmosismembranes known as nanofiltration membranes. Nanofiltration membraneshave larger “pores” than other composite polyamide reverse osmosismembranes and exhibit a low rejection rate of monovalent salts whileexhibiting a high rejection rate of divalent salts and organic materialshaving a molecular weight greater than 300. Nanofiltration membranes aretypically used to remove calcium and magnesium salts from water, i.e.,to soften hard water, and to remove natural organic matter, such ashumic acids from decaying plant leaves, from water. Humic acid isnegatively charged at a pH above 6 and can be adsorbed on the membranethrough hydrophobic interactions with the membrane surface.)

The polyfunctional amine reactant is typically present in an aqueoussolution in an amount in the range of from about 0.1 to 20%, preferably0.5 to 8%, by weight, of the aqueous solution. The pH of the aqueoussolution is in the range of from about 7 to 13. The pH can be adjustedby the addition of a basic acid acceptor in an amount ranging from about0.001% to about 5%, by weight, of the solution. Examples of theaforementioned basic acid acceptor include hydroxides, carboxylates,carbonates, borates, phosphates of alkali metals, and trialkylamines.

In addition to the aforementioned polyfunctional amine reactant (and, ifdesired, the aforementioned basic acid acceptor), the aqueous solutionmay further comprise additives of the type described in the patentsincorporated herein by reference, such additives including, for example,polar solvents, amine salts and polyfunctional tertiary amines (eitherin the presence or absence of a strong acid).

The polyfunctional amine-reactive reactant employed in the presentinvention is one or more compounds selected from the group consisting ofa polyfunctional acyl halide, a polyfunctional sulfonyl halide and apolyfunctional isocyanate. Preferably, the polyfunctional amine-reactivereactant is an essentially monomeric, aromatic, polyfunctional acylhalide, examples of which include di- or tricarboxylic acid halides,such as trimesoyl chloride (TMC), isophthaloyl chloride (IPC),terephthaloyl chloride (TPC) and mixtures thereof. Examples of otherpolyfunctional amine-reactive reactants are disclosed in the patentsincorporated herein by reference.

The polyfunctional amine-reactive reactant is typically present in anorganic solvent solution, the solvent for said organic solvent solutioncomprising any organic liquid immiscible with water. The polyfunctionalamine-reactive reactant is typically present in the organic liquid in anamount in the range of from about 0.005 to 5 wt % preferably 0.01 to 0.5wt % of the solution. Examples of the aforementioned organic liquidinclude hexane, cyclohexane, heptane, alkanes having from 8 to 12 carbonatoms, and halogenated hydrocarbons, such as the FREON series. Otherexamples of the above-described organic liquid may be found in thepatents incorporated herein by reference. Preferred organic solvents arealkanes having from 8 to 12 carbon atoms and mixtures thereof. ISOPAR®solvent (Exxon Corp.) is such a mixture of alkanes having from 8 to 12carbon atoms.

The hydrophilic coating of the present invention is formed by covalentlybonding a hydrophilic compound of the type described below to residualacid chlorides of the polyamide membrane.

According to a first aspect of the invention, said hydrophilic compoundincludes (i) at least one reactive group adapted to covalently bonddirectly to the polyamide membrane, said at least one reactive groupbeing at least one of a primary amine and a secondary amine; (ii) atleast one non-terminal hydroxyl group; and (iii) at least one amidegroup.

According to a first embodiment of said first aspect, the aforementionedhydrophilic compound may be a compound represented by the formula I:

R₁—(CHOH)₁—CONR₄—R₂—NHR₃  (I)

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of an alkyl group having carbon atoms ranging from 2 to 12, analkenyl group having at least one double bond and carbon atoms rangingfrom 2 to 12, a cyclohexyl group, a phenylene group, a xylylene group,and a cyclohexanebismethyl group, wherein R₃ is one of hydrogen, analkyl group having carbon atoms ranging from 1 to 4, and an alkenylgroup having at least one double bond and carbon atoms ranging from 2 to4, wherein R₄ is one of hydrogen, a methyl group, an ethyl group, and apropyl group, and wherein l is an integer ranging from 1 to 10.

Examples of compounds encompassed by Formula I includeN-(2-aminoethyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(3-aminopropyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(4-aminobutyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(5-aminopentyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(6-aminohexyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(2-aminoethyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(3-aminopropyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(4-aminobutyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(5-aminopentyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide, andN-(6-aminohexyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide.

According to a second embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula II:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), and whereinl is an integer ranging from 1 to 10.

According to a third embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula III:

R₁—(CHOH)₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (III)

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of hydrogen, an alkyl group having carbon atoms ranging from 1 to4, and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of hydrogen, a methyl group, anethyl group, and a propyl group, wherein l is an integer ranging from 1to 10, wherein m is an integer ranging from 1 to 1000, and wherein n isan integer ranging from 2 to 6.

Examples of compounds encompassed by Formula III includeN-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6,7-hexahydroxyheptanamide,N-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(13-amino-4,7,10-trioxamidecyl)-2,3,4,5,6,7-hexahydroxyheptanamide,andN-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide.

According to a fourth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula IV:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of hydrogen, an alkyl group having carbon atoms ranging from 1 to4, and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of a methyl group and an ethylgroup, wherein R₄ is one of hydrogen, a methyl group, an ethyl group,and a propyl group, wherein l is an integer ranging from 1 to 10, andwherein m is an integer ranging from 1 to 100.

According to a fifth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula V:

R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH₂O)_(m)—CH₂CH(OH)CH₂—NHR₂  (V)

wherein R₁ is one of hydrogen, a methyl group, and an ethyl group,wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 1000.

According to a sixth embodiment of said first aspect, the hydrophiliccompound may be a compound represented by the formula VI:

R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH(CH₃)O)_(m)—CH₂CH(OH)CH₂—NHR₂  (VI)

wherein R₁ is one of hydrogen, a methyl group, and an ethyl group,wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 100.

According to a second aspect of the invention, the hydrophilic compoundincludes (i) at least one reactive group adapted to covalently bonddirectly to the polyamide membrane, said at least one reactive groupbeing at least one of a primary amine and a secondary amine; (ii) ahydroxyl group; and (iii) an amide group; (iv) wherein the hydroxylgroup and the amide group are linked directly to one another by one ofan alkyl group and an alkenyl group.

According to a first embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula VII:

HO—R₁—CONR₄—R₂—NHR₃  (VII)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is an alkyl group having carbonatoms ranging from 2 to 6, an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 6, a cyclohexyl group, aphenylene group, a xylylene group, and a cyclohexanebismethyl group,wherein R₃ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₄ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein NR₄—R₂—NHR₃ can be replaced with a piperazinyl group.

According to a second embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula VIII:

HO—R₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (VIII)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is one of hydrogen, an alkyl grouphaving carbon atoms ranging from 1 to 4, and an alkenyl group having atleast one double bond and carbon atoms ranging from 2 to 4, wherein R₃is one of hydrogen, a methyl group, an ethyl group, and a propyl group,wherein m is an integer ranging from 1 to 1000, and wherein n is aninteger ranging from 2 to 6.

According to a third embodiment of said second aspect, the hydrophiliccompound may be a compound represented by formula IX:

HO—R₁—CONR₃—(CH₂CH(CH₃)O)_(m)—CH₂CH(CH₃)—NHR₂  (IX)

wherein R₁ is one of an alkyl group having carbon atoms ranging from 1to 4 and an alkenyl group having at least one double bond and carbonatoms ranging from 2 to 4, wherein R₂ is one of hydrogen, an alkyl grouphaving carbon atoms ranging from 1 to 4, and an alkenyl group having atleast one double bond and carbon atoms ranging from 2 to 4, wherein R₃is one of hydrogen, a methyl group, an ethyl group, and a propyl group,and wherein m is an integer ranging from 1 to 100.

The hydrophilic compound described above is covalently bonded to theresidual acid chlorides of the polyamide membrane by contacting thepolyamide membrane with an aqueous solution comprising the hydrophiliccompound. The hydrophilic compound is typically present in the aqueoussolution in an amount ranging from about 0.0001 wt % to 8 wt % of theaqueous solution, preferably about 0.001 wt % to 4 wt % of the aqueoussolution.

In accordance with the teachings of the present invention, a compositepolyamide reverse osmosis membrane having a high fouling resistance maybe made as follows: First, the above-described porous support is coatedwith the above-described aqueous solution utilizing either a handcoating or a continuous operation, and the excess solution is removedfrom the support by rolling, sponging, air knifing or other suitabletechniques. Following this, the coated support material is thencontacted, for example, by dipping or spraying, with the above-describedorganic solvent solution and allowed to remain in place for a period oftime in the range of from about 5 seconds to about 10 minutes,preferably about 20 seconds to 4 minutes. The resulting product is thendried at a temperature below 50° C., preferably by air-drying at roomtemperature, for about 1 minute. The hydrophilic coating of the presentinvention is then formed on the polyamide membrane by contacting, forexample, by dipping or by spraying, the thus-formed polyamide membranewith an aqueous solution of the above-described hydrophilic compound fora period in the range of about 5 seconds to about 10 minutes, preferablyabout 20 seconds to 4 minutes, at a temperature of about roomtemperature to 95° C., whereby said hydrophilic compound covalentlybonds to the polyamide membrane through the reaction of the primary orsecondary amino group with the residual acid chloride of the polyamidemembrane. The resulting product is then rinsed in a basic aqueoussolution, such as 0.2% sodium carbonate, from about 1 to 30 minutes atroom temperature to 95° C., and then rinsed with deionized water.

As noted above, the hydrophilic coating of the present invention is notlimited to use with composite polyamide reverse osmosis membranes butcan also be applied directly to conventional microporous membranes, suchas microfiltration membranes and ultrafiltration membranes, to helpresist fouling thereof by proteins, macromolecules and colloids whensuch membranes are used in surface water treatment, protein separations,and food and beverage processing. A conventional microfiltrationmembrane is typically a microporous support of the type described abovethat has a pore size of about 0.1μ-10μ. A conventional ultrafiltrationmembrane is typically a microporous support of the type described abovethat has a pore size of about 0.001μ-0.05μ.

The following examples are provided for illustrative purposes only andare in no way intended to limit the scope of the present invention:

Example 1

A 140 μm thick microporous polysulfone support including the backingnon-woven fabric was soaked in an aqueous solution containing 2 wt % ofmeta-phenylenediamine (MPD) and 0.2 wt % 2-ethyl-1,3-hexanediol for 40seconds. The support was drained and nip rolled to remove the excessaqueous solution. Then, the coated support was dipped in 0.1 wt %solution of trimesoyl chloride (TMC) in Isopar® solvent (Exxon Corp.)for 1 minute followed by draining the excess organic solution off thesupport. The resulting composite membrane was air-dried for about 1minute and then soaked at room temperature for 2 minutes in a mixture of0.03 wt % of N-(2-aminoethyl)-2,3,4,5,6-pentahydroxyhexanamide (AEPH)and 0.05% Na₂CO₃ in deionized water. AEPH was made from the reaction ofethylenediamine with gluconic acid lactone in a 1:1 molar ratio in waterat room temperature for 24 hours. The resulting product was then rinsedin 0.2% Na₂CO₃ aqueous solution for 30 minutes at room temperature, andthen rinsed in deionized water.

The initial performance of the membrane was measured by passing anaqueous solution containing 2000 ppm of NaCl through the membrane in acrossflow mode at 225 psi and 25° C. The salt rejection was 99.5% andthe flux was 32.5 gfd. The fouling resistance of the membrane was thenevaluated under the same conditions described above by further adding 50ppm dry milk to the feed water at a pH of 6.4. (The protein of dry milkin an aqueous solution may exist as protein molecules and colloids,i.e., aggregates of protein molecules, and can be adsorbed to themembrane through hydrophobic interactions with the membrane surface.)After circulating the feed water through the membrane for 2 hours, thesalt rejection was 99.7% and the flux was 28.1 gfd.

Example 2

The same procedure as set forth in Example 1 was carried out for Example2, except that 0.05 wt % of AEPH and 0.05% Na₂CO₃ in deionized waterwere used. The performance of the resulting membrane under the sameconditions described above for Example 1 is shown below in Table I.

Example 3

The same procedure as set forth in Example 1 was carried out for Example3, except that 0.03 wt %N-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6-pentahydroxyhexanamide (ADOPH) wasused, instead of 0.03 wt % AEPH. ADOPH was made from the reaction of2,2′-(ethylenedioxy)bis(ethylamine) with gluconic acid lactone in a 1:1molar ratio in water at room temperature for 24 hours.

The performance of the resulting membrane under the same conditionsdescribed above for Example 1 is shown below in Table I.

Example 4

The same procedure as set forth in Example 1 was carried out for Example4, except that 0.05 wt % ADOPH was used, instead of 0.03 wt % AEPH. Theperformance of the resulting membrane under the same conditionsdescribed above for Example 1 is shown below in Table I.

Example 5

The same procedure as set forth in Example 1 was carried out for Example5, except that 0.03 wt %N-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6-pentahydroxyhexanamide(ATOPH) was used, instead of 0.03 wt % AEPH. The performance of theresulting membrane under the same conditions described above for Example1 is shown below in Table I.

Example 6

The same procedure as set forth in Example 1 was carried out for Example6, except that 0.05% ATOPH was used, instead of 0.03 wt % AEPH. Theperformance of the resulting membrane under the same conditionsdescribed above for Example 1 is shown below in Table I.

Comparative Example 1

The same procedure as set forth in Example 1 was carried out forComparative Example 1, except that no hydrophilic coating was applied tothe composite membrane. The initial salt rejection was 99%, and theinitial flux was 27.1 gfd. When subjected to the same fouling conditionsof Example 1, the salt rejection was 99.5%, and the flux was 21.2 gfd asshown in Table 1.

TABLE I Initial Salt Final Flux in the Rejection Initial Flux presenceof dry Flux Decline Membrane (%) (gfd) milk (gfd) (%) Example 1 99.532.5 28.1 13.5 Example 2 99.6 30.8 27.4 10.9 Example 3 99.3 22.3 20.29.4 Example 4 99.4 19.7 18.6 5.5 Example 5 99.4 19.2 18.2 5.2 Example 699.6 18.3 17.8 2.7 Comparative 99.0 27.1 21.2 21.8 Example 1

As can be seen from Table I, the coated membranes of Examples 1-6 allexhibited a considerably smaller decrease in flux in the presence of thefouling agent (50 ppm dry milk) than did the uncoated membrane(Comparative Example 1). This is advantageous because, as noted above, aconsistency in flux over a long period of time is highly desirable sinceit obviates the need to continuously vary the operating pressure and towash the membrane to remove fouling agents therefrom. It should also berecognized that, whereas the final flux in the present case was measuredonly after two hours of use, such membranes are expected to becontinuously used for considerably longer periods of time. Accordingly,the final flux values given above are much more representative of theflux properties of the membranes over their respective lifetimes of usethan are the initial flux values.

Also, it should be noted that, when the coated membranes were washedfollowing their two-hour period of use, their respective fluxessubstantially returned to their initial fluxes whereas the untreatedmembrane, when washed following its two-hour period of use, onlyapproached about 85% of its initial flux.

The embodiments of the present invention recited herein are intended tobe merely exemplary and those skilled in the art will be able to makenumerous variations and modifications to it without departing from thespirit of the present invention. All such variations and modificationsare intended to be within the scope of the present invention as definedby the claims appended hereto.

1. A composite polyamide reverse osmosis membrane, said compositepolyamide reverse osmosis membrane comprising: (a) a microporoussupport; (b) a polyamide layer on said microporous support; and (c) ahydrophilic coating on said polyamide layer, said hydrophilic coatingbeing formed by covalently bonding a hydrophilic compound to thepolyamide membrane, wherein said hydrophilic compound includes (i) atleast one reactive group adapted to covalently bond directly to thepolyamide membrane, said at least one reactive group being at least oneof a primary amine and a secondary amine; (ii) at least one non-terminalhydroxyl group; and (iii) at least one amide group.
 2. The compositepolyamide reverse osmosis membrane as claimed in claim 1 wherein saidhydrophilic compound is a compound represented by formula I:R₁—(CHOH)₁—CONR₄—R₂—NHR₃  (I) wherein R₁ is one of an aldehyde group(—CHO), a carboxylic acid group (—COOH), a nitrile group and ahydroxymethyl group (—CH₂OH), wherein R₂ is one of an alkyl group havingcarbon atoms ranging from 2 to 12, an alkenyl group having at least onedouble bond and carbon atoms ranging from 2 to 12, a cyclohexyl group, aphenylene group, a xylylene group, and a cyclohexanebismethyl group,wherein R₃ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₄ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein l is an integer ranging from 1 to
 10. 3. The composite polyamidereverse osmosis membrane as claimed in claim 2 wherein said hydrophiliccompound is selected from the group consisting ofN-(2-aminoethyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(3-aminopropyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(4-aminobutyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(5-aminopentyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(6-aminohexyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(2-aminoethyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(3-aminopropyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(4-aminobutyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(5-aminopentyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide, andN-(6-aminohexyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide.
 4. The compositepolyamide reverse osmosis membrane as claimed in claim 3 wherein saidhydrophilic compound isN-(2-aminoethyl)-2,3,4,5,6-pentahydroxyhexanamide.
 5. The compositepolyamide reverse osmosis membrane as claimed in claim 1 wherein saidhydrophilic compound is a compound represented by formula II:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), and whereinl is an integer ranging from 1 to
 10. 6. The composite polyamide reverseosmosis membrane as claimed in claim 1 wherein said hydrophilic compoundis a compound represented by formula III:R₁—(CHOH)₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (III) wherein R₁ is oneof an aldehyde group (—CHO), a carboxylic acid group (—COOH), a nitrilegroup and a hydroxymethyl group (—CH₂OH), wherein R₂ is one of hydrogen,an alkyl group having carbon atoms ranging from 1 to 4, and an alkenylgroup having at least one double bond and carbon atoms ranging from 2 to4, wherein R₃ is one of hydrogen, a methyl group, an ethyl group, and apropyl group, wherein l is an integer ranging from 1 to 10, wherein m isan integer ranging from 1 to 1000, and wherein n is an integer rangingfrom 2 to
 6. 7. The composite polyamide reverse osmosis membrane asclaimed in claim 6 wherein said hydrophilic compound is selected fromthe group consisting ofN-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6,7-hexahydroxyheptanamide,N-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide,N-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6-pentahydroxyhexanamide,N-(13-amino-4,7,10-trioxamidecyl)-2,3,4,5,6,7-hexahydroxyheptanamide,andN-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6,7,8-heptahydroxyoctanamide.8. The composite polyamide reverse osmosis membrane as claimed in claim7 wherein said hydrophilic compound is selected from the groupconsisting ofN-(8-amino-3,6-dioxaoctyl)-2,3,4,5,6-pentahydroxyhexanamide andN-(13-amino-4,7,10-trioxamideyl)-2,3,4,5,6-pentahydroxyhexanamide. 9.The composite polyamide reverse osmosis membrane as claimed in claim 1wherein said hydrophilic compound is a compound represented by formulaIV:

wherein R₁ is one of an aldehyde group (—CHO), a carboxylic acid group(—COOH), a nitrile group and a hydroxymethyl group (—CH₂OH), wherein R₂is one of hydrogen, an alkyl group having carbon atoms ranging from 1 to4, and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of a methyl group and an ethylgroup, wherein l is an integer ranging from 1 to 10, wherein R₄ is oneof hydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to
 100. 10. The compositepolyamide reverse osmosis membrane as claimed in claim 1 wherein saidhydrophilic compound is a compound represented by formula V:R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH₂O)_(m)—CH₂CH(OH)CH₂—NHR₂  (V) wherein R₁is one of hydrogen, a methyl group, and an ethyl group, wherein R₂ isone of hydrogen, an alkyl group having carbon atoms ranging from 1 to 4,and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of hydrogen, a methyl group, anethyl group, and a propyl group, and wherein m is an integer rangingfrom 1 to
 1000. 11. The composite polyamide reverse osmosis membrane asclaimed in claim 1 wherein said hydrophilic compound is a compoundrepresented by formula VI:R₁—CONR₃—CH₂CH(OH)CH₂O—(CH₂CH(CH₃)O)_(m)—CH₂CH(OH)CH₂—NHR₂  (VI) whereinR₁ is one of hydrogen, a methyl group, and an ethyl group, wherein R₂ isone of hydrogen, an alkyl group having carbon atoms ranging from 1 to 4,and an alkenyl group having at least one double bond and carbon atomsranging from 2 to 4, wherein R₃ is one of hydrogen, a methyl group, anethyl group, and a propyl group, and wherein m is an integer rangingfrom 1 to
 100. 12. A composite polyamide reverse osmosis membrane, saidcomposite polyamide reverse osmosis membrane comprising: (a) amicroporous support; (b) a polyamide layer on said microporous support;and (c) a hydrophilic coating on said polyamide layer, said hydrophiliccoating being formed by covalently bonding a hydrophilic compound to thepolyamide membrane, wherein said hydrophilic compound includes (i) atleast one reactive group adapted to covalently bond directly to thepolyamide membrane, said at least one reactive group being at least oneof a primary amine and a secondary amine; (ii) a hydroxyl group; and(iii) an amide group; (iv) wherein the hydroxyl group and the amidegroup are linked directly to one another by one of an alkyl group and analkenyl group.
 13. The composite polyamide reverse osmosis membrane asclaimed in claim 12 wherein said alkyl group is an alkyl group havingcarbon atoms ranging from 1 to 4 and wherein said alkenyl group is analkenyl group having at least one double bond and carbon atoms rangingfrom 2 to
 4. 14. The composite polyamide reverse osmosis membrane asclaimed in claim 12 wherein said hydrophilic compound is a compoundrepresented by formula VII:HO—R₁—CONR₄—R₂—NHR₃  (VII) wherein R₁ is one of an alkyl group havingcarbon atoms ranging from 1 to 4 and an alkenyl group having at leastone double bond and carbon atoms ranging from 2 to 4, wherein R₂ is analkyl group having carbon atoms ranging from 2 to 6, an alkenyl grouphaving at least one double bond and carbon atoms ranging from 2 to 6, acyclohexyl group, a phenylene group, a xylylene group, and acyclohexanebismethyl group, wherein R₃ is one of hydrogen, an alkylgroup having carbon atoms ranging from 1 to 4, and an alkenyl grouphaving at least one double bond and carbon atoms ranging from 2 to 4,wherein R₄ is one of hydrogen, a methyl group, an ethyl group, and apropyl group, and wherein NR₄—R₂—NHR₃ can be replaced with a piperazinylgroup.
 15. The composite polyamide reverse osmosis membrane as claimedin claim 12 wherein said hydrophilic compound is a compound representedby formula VIII:HO—R₁—CONR₃—(CH₂CH₂O)_(m)—(CH₂)_(n)—NHR₂  (VIII) wherein R₁ is one of analkyl group having carbon atoms ranging from 1 to 4 and an alkenyl grouphaving at least one double bond and carbon atoms ranging from 2 to 4,wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, wherein mis an integer ranging from 1 to 1000, and wherein n is an integerranging from 2 to
 6. 16. The composite polyamide reverse osmosismembrane as claimed in claim 12 wherein said hydrophilic compound is acompound represented by formula IX:HO—R₁—CONR₃—(CH₂CH(CH₃)O)_(m)—CH₂CH(CH₃)—NHR₂  (IX) wherein R₁ is one ofan alkyl group having carbon atoms ranging from 1 to 4 and an alkenylgroup having at least one double bond and carbon atoms ranging from 2 to4, wherein R₂ is one of hydrogen, an alkyl group having carbon atomsranging from 1 to 4, and an alkenyl group having at least one doublebond and carbon atoms ranging from 2 to 4, wherein R₃ is one ofhydrogen, a methyl group, an ethyl group, and a propyl group, andwherein m is an integer ranging from 1 to 100.